Thin film transistors (TFTs) can be used to determine the bulk-like mobilities of amorphous semiconductors. Different organic hole transporters (HTs) are under investigation including spiro-TPD, 2TNATA, NPB and TPD which are commonly used in organic light-emitting diodes (OLEDs). In addition, we also measure the TFT hole mobilities of two iridium phosphors: Ir(ppy)3 and Ir(piq)3. These materials were grown on two different gate dielectric surfaces which were SiO2 and polystyrene (PS). On SiO2, the TFT mobilities are found to be 1-2 orders smaller than the bulk hole mobilities as evaluated independently by time-of-flight (TOF) technique. On the other hand, on PS gate dielectric layer, the TFT mobilities of these hole transporters are found to be in good agreement with TOF data. A thickness dependence measurement was carried out on TFT with PS. We found that only 10nm of organic semiconductor is sufficient for TFTs to achieve TOF mobilities. We further investigate why organic semiconductors on SiO2 have such huge reduction of mobilities. Temperature dependent mobility measurements were carried out and the data were analyzed by the Gaussian Disorder Model (GDM). We found that on SiO2 surface, when compared to the bulk values, the energetic disorders (σ) of the HTs increase and simultaneously, the high temperature limits (∞) of the carrier mobilities decrease. Both σ and ∞ contribute to the reduction of the carrier mobility. The increase in σ is related to the presence of randomly oriented polar Si-O bonds. The reduction of ∞ is topological in origin and is related to the orientations of the more planar molecules on SiO2. The more planar molecules tend to lie horizontally on the surface and such orientation is unfavorable for charge transport in TFT configuration. Hybrid organic/inorganic perovskites have emerged as an outstanding material for photovoltaic cells. In the second part of this work, we setup a repeatable perovskite recipe and optimized the system under different conditions. Under certain circumstances, a perovskite solar cell with power conversion efficiency ~9% can be achieved with PEDOT:PSS as hole transporting layer with the conventional structure.

A systematic study of the crystallization of terthiophene, chosen as a model compound, has been carried out using the thermal gradient technique. We have observed that nucleation and growth can be decoupled for organic semiconductors (OSC) crystallizing from the melt in a temperature gradient and that these conditions lead to the generation of highly textured thin films with uniaxial in-plane alignment. Furthermore, adequate gradient conditions allow the selective growth of a single polymorphic form of terthiophene. The last results obtained on terthiophene concern the orientation of the unit cell with the reciprocal vector c* normal to the substrate and the alignment of the [100] and [-100] directions parallel to the gradient direction. It is hypothesized that the geometry of the system and the temperature profile induce a preferential fast growth direction perpendicular to the gradient direction.<p>In order to validate these results, we embarked on an exploratory study of the crystallization of a set of organic semiconductors, carefully selected based on rational arguments, to evaluate the potential of the thermal gradient process as well as the required parameters for an OSC to perform adequately in this treatment. As in the case of terthiophene, nucleation and growth can be decoupled for the other organic semiconductors depending on their rate of growth. Furthermore, we have been able to reproduce on another polymorphic compound the selective growth of a single polymorphic form by applying adequate gradient conditions. We have also observed that compounds tend to orient preferentially along one of their major morphological planes parallel to the substrate, indicating a heterogeneous nucleation mechanism. A careful comparison between the different samples allowed us to confirm and complete our growth mechanism proposition. Based on the undercooling, maximal growth rate, primary and secondary nucleation rates of the compound, geometry of the system and adequate gradient parameters, a preferential alignment of the crystals along the thermal gradient direction can be achieved. Finally, we showed through this investigation and careful comparison that 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene possesses all the characteristics to be an excellent material candidate for the thermal gradient processing: low primary nucleation rate, moderate undercooling, high growth rate, platelet-like crystal growth morphology and liquid crystal phase allowing preorganization of the compound before crystallization and processing on single substrates without dewetting. Moreover, this compound is currently one of the best solution processable organic semiconductors.<p>We then investigated the directional crystallization of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene directly from its liquid crystal phase as a function of thermal gradient parameters (magnitude of the gradient, sample velocity) and film thicknesses in thin film geometry (spin-coated films). Again, decoupling of the nucleation and growth has been observed for crystallization processed directly from the liquid crystal phase leading to the generation of highly textured films presenting uniaxial in-plane alignments of the crystallites. Moreover, secondary nucleation spots highlighted by POM in the alignment region give a clue to elucidate the alignment mechanism. The unit cell orients with the reciprocal vector c* normal to the substrate. Moreover, POM observation tends to indicate systematic thermal cracks orientations for higher rates of displacement (25 μm.s-1) as well as a reduction of the number of domains present in the sample, suggesting a preferential alignment of the crystallites at higher rates of displacement. All our results indicate that an optimum of the quality of the aligned film is reached for thermal gradient conditions of 120 °C - 90 °C - 25 μm.s-1. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Le developpement des transistors a effet de champ organiques est limite par les performances des semi-conducteurs organiques disponibles sur le marche, la mobilite des charges electriques (mu) atteinte de maniere reproductible est de 1cm2/Vs. Un des principaux frein est la presence de defauts lies a l'organisation moleculaire. Les oligothiophenes sont a l'heure actuelle parmis les semi-conducteurs organiques les plus performants, c'est pourquoi nous avons decide de baser notre recherche sur des derives du terthiophenes et du quaterthiophene. Ces composes s'organisent de maniere a permettre une conduction a deux dimensions. Mais la mobilite de charge est limitee par des defauts de plan au sein du reseau moleculairemais aussi aux defauts dus aux irregularite de l'interface dielectrique/semi-conducteur.<p>Afin de remedier a ce probleme, nous avons envisage deux approche: l'une pour la diminution des defauts de plan par l'utilisation de phase cristal liquides; l'autre vise la diminution des defauts dus aux irregularites de la surface du substrat, par l'utilisation de systemes pi relies par un pont covalent.<p>Les 5,5'-dialkylterthiophenes (chaines allant du propyle au dodecyle) et le 5,5'- dihexylquaterthiophene sont conus pour former des phases cristal liquides. Mais ces dernieres n'apparaissent cependant qu'a des temperatures superieures a 45degC. LEs chaines alkyles utilisees etant toutes des chaines lineaires, notre premiere idee a ete de synthetiser de nouveaux derives avec des chaines alkyles ou alkenyles branchees. Une voie de synthese 'one-pot' permettant de varier aisement les chaines alkyles greffees dans les positions alfa et beta des bi-, ter- et quaterthiophene a ete mise au point. La reaction d'alkylation se fait en presence de n-BuLi et t-BuOK avec des rendements variant entre 80 et 90%. LEs composes obtenus par cette methode ne presentent pas les proprietes requises, c'est pourquoi une nouvelle modification structurale a ete envisagee: la dyssymetrisation. Cette fois les chaines greffees sur les positions alfa et beta sont differentes. De nouvelles voies de synthese ont ete etablies dans ce but. Elles sont basees sur l'heterocouplage de Suzuki qui va permettre la formation d'un lien carbone-carbone entre deux unites oligothiophenes. Ce couplage donne des rendements compris entre 35 et 65%. <p>Notre connaissance de la formation de comnposes dissymetriques va etre directement appliquee a la formation des unites oligothiophenes reliees par un pont covalent. Quelque soit la nature du pont, il est necessaire de passer par un oligothiophene subtsitue en position alfa et pas omega. Deux types de ponts covalents ont ete utilises, un pont etylene et un pont disulfure, ce qui a requis la mise au point de deux schemas de synthese differents. POur les composes possendant un pont ethylene, un des synthon comporte deja un pont, l'etape finale consiste en un couplage de Suzuki. En ce qui concerne les derives possedant un pont sulfure, la formation du pont se fait lors de la derniere etape. <p><p>Les proprietes thermotropes de tous les composes synthetises ont ete mesurees, cela nous a permis de faire une etude comparative dans le but de relier la structure aux proprietes thermotropes. La taille du corps aromatique, la longueur des chaines alkyles, la presence de branchements, d'insaturations sur les chaines laterales, de meme que la dissymetrisation ont ete etudies. Nous avons tentes de correler l'evolution des proprites thermotropes de nos composes avec l'evolution des temperatures de fusion des alcanes et alcenes correspondant. Cela donne de bons resultats pour les derives du terthiophenes, mais l'augmentation de la taille du corps aromatique complique fortement les resultats, LEs constatations les plus importantes sont que la presence de branchements sur les chaines alkyles provoque la diminution des temperatures de transistions des terthiophenes et des quaterthiophenes. Meme si en plus, ces branchements provoquent la perte du caractere fluide pour les terthiophenes. Il est incontestable que la methode qui permet de modifier de facon plus fine les temperatures de transition est la dissymetrisation. Cela nous permet d'obtenir des composes possedant les proprietes rechercheesa a savoir une phase cristal liquide a temperature ambiante. Sans toutefois comprendre le lien subtil entre la structure moleculaire et les proprietes thermotropes. <p>Afin de comprendre les proprietes de semi-conduction des composes synthetises, nous avons fabriques des transistors a effet de champ avec trois d'entre eux; le 5,5'-dihexylquaterthiophene sert de compose modele, un derive du quaterthiophene possedant une phase cristal liquide a temperature ambiante et derive compose de deux unites hexylquaterthiophene relies par un pont ethylene. Les resultats pour le compose presentant une phase cristal liquide sont peu concluants. IL ne montre aucune proprietes de semi-conduction, ce qui peut s'expliquer par la difference de longueur des chaines alkyles greffees ,qui induit un deplacement lateral defavorable au transport de charges. Pour le compose ponte une mobilite de charge de 0.015cm2/V.s. a ete mesuree ( compose de reference 0.013 cm2/V.s.) avec un dielectrique de rugosite nulle. Nous pouvons conclure que le compose ponte possede bien les proprietes de semi-conduction desirees. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

It is well established that the morphology and physical properties of an organic semiconducting (OSC) material regulate its electronic properties. However, structure-function relationships remain difficult to describe in polymer-based OSC, which are of particular interest due to their robust mechanical properties. If relationships among the molecular and bulk levels of structure can be found, they can aid in the design of improved materials. To explore and detail important structure-function relationships in polymer-based OSC, this work employs molecular dynamics (MD) simulations to study various π-conjugated polymers in different environments. Two independent investigations are discussed in this work. One investigation examines how the purposeful disruption of the π-conjugated backbone to increase the chain flexibility impacts the chain structure and packing in the condensed phase. This is done by adding a conjugation break spacer (CBS) unit of one to ten carbons in length into the monomer structure of diketopyrrolopyrrole-based polymers. It is found that trends in the folding and glass structure follow the increase and the parity (odd versus even) of the CBS length. The second investigation analyzes a variety of polymers and small molecule acceptor (SMA) blends to observe the effects of changing the shape of either component and the physical properties of the material, as well as the structure of the polymer chains. It is found that the conjugated core, the side chains, and the planarity or sphericity each influence the density and diffusion of the materials made.

Studium nových materiálů potenciálně využitelných pro organickou elektroniku a fotoniku získává velmi důležitý význam z hlediska ekologie. Tato práce je zaměřena na studium vlastností biologických materiálů, které by našly uplatnění v aplikační sféře. Zájem o znalosti v oblasti základních a pokročilých vlastností organických a biologických materiálů, které mohou být potenciálně využity v oblasti organické elektroniky a fotoniky přináší nové otázky, které mohou přispět k rozvoji této oblasti. Ke studiu základních procesů souvisejících s optickými a elektrickými vlastnostmi materiálů, jako je například přenos náboje, jsme využili různé techniky a metody charakterizace. První část práce je zaměřena na souhrn vlastností anorganických a organických materiálů umožňující jejich možné využití v organické elektronice a fotonice, druhá část práce poskytuje nejnovější přehled z oblasti pokročilých biologických materiálů a jejich vlastností související se záměrem této práce. Třetí část práce pak shrnuje experimentální metody a shrnuje získané výsledky. Nakonec je diskutován vztah mezi pozorovanými jevy a strukturou studovaných materiálů na molekulární úrovni.

The work contains literature search on organic electronics, especially organic solar cells. There is described in detail their principle of function and used materials. Also there are mentioned possibilities of synthesis of conjugated systems for this applications and methods of their structural, optical and electrical characterization. In experimental section and discussion is introduced synthesis of five new, various substituted derivates of benzylidenaniline and their characterisation together with another seven derivates, whose synthesis has been described in bachelor thesis. There is investigated influence of substituents to chemical shift of hydrogen on imine bridge and to position of absorption peaks in UV-Vis spectra. There also has been found method for fabrication of thin layers and solar cells with bulk heterojunction have been fabricated. Next, V-A characteristics and impedance spectra of the cells were recorded. According to obtained results, investigated systems act as photodiodes and in case of three derivates the photoinduced increase of electric current has been observed. But for application in solar cells it is necessary to shift the position of absorption spectra towards longer wavelengths.

Using photoelectron spectroscopy, we show measurements of energy level alignment of organic semiconducting layers. The main focus is on the properties and the influence of doped layers. The investigations on the p-doping process in organic semiconductors show typical charge carrier concentrations up to 2*10E20 cm-3. By a variation of the doping concentration, an over proportional influence on the position of the Fermi energy is observed. Comparing the number of charge carriers with the amount of dopants present in the layer, it is found that only 5% of the dopants undergo a full charge transfer. Furthermore, a detailed investigation of the density of states beyond the HOMO onset reveals that an exponentially decaying density of states reaches further into the band gap than commonly assumed. For an increasing amount of doping, the Fermi energy gets pinned on these states which suggests that a significant amount of charge carriers is present there. The investigation of metal top and bottom contacts aims at understanding the asymmetric current-voltage characteristics found for some symmetrically built device stacks. It can be shown that a reaction between the atoms from the top contact with the molecules of the layer leads to a change in energy level alignment that produces a 1.16eV lower electron injection barrier from the top. Further detailed investigations on such contacts show that the formation of a silver top contact is dominated by diffusion processes, leading to a broadened interface. However, upon insertion of a thin aluminum interlayer this diffusion can be stopped and an abrupt interface is achieved. Furthermore, in the case of a thick silver top contact, a monolayer of molecules is found to float on top of the metal layer, almost independent on the metal layer thickness. Finally, several device stacks are investigated, regarding interface dipoles, formation of depletion regions, energy alignment in mixed layers, and the influence of the built-in voltage. We show schematic energy level alignments of pn junctions, pin homojunctions, more complex pin heterojunctions with Zener-diode characteristics, as well as a complete OLED stack. The results allow a deeper insight in the working principle of such devices. / Mit Hilfe der Photoelektronenspektroskopie werden in der vorliegenden Arbeit Energieniveaus an Grenzflächen von organischen Halbleitern untersucht, wobei ein Hauptaugenmerk auf dem Einfluss und den Eigenschaften dotierter Schichten liegt. Bei der Untersuchung grundlegender Eigenschaften eines p-dotierten organischen Halbleiters können Ladungsträgerkonzentrationen bis zu 2*10E20 cm-3 nachgewiesen werden. Eine Variation der Dotierkonzentration zeigt einen überproportionalen Einfluss der Ladungsträger auf die Position des Ferminiveaus verglichen mit Experimenten an anorganischen Schichten. Durch den Vergleich mit der Anzahl Dotanden in der Schicht kann gezeigt werden, dass dabei nur etwa 5% der Dotanden einen vollständigen Ladungstransfer eingehen. Eine detaillierte Untersuchungen der Zustandsdichte jenseits des HOMOs (Highest Occupied Molecular Orbital) zeigt, dass die exponentiell abfallende Flanke der Zustandsdichte weiter in die Bandlücke hineinreicht als üblicherweise angenommen. Das Ferminiveau erfährt bei steigender Dotierung ein Pinning an diesen Zuständen, was für eine signifikante Ladungsträgerkonzentration spricht. Weiterhin wurden Untersuchungen zu Metal Top- und Grundkontakten durchgeführt. Es kann gezeigt werden, dass die Ursache für die Entstehung unsymmetrischer Strom-Spannungskurven, trotz eines symmetrischen Probenaufbaus, an einer Reaktion zwischen dem Molekül und den Metallatomen liegt. Dadurch entsteht eine um 1.16eV reduzierte Injektionsbarriere für Elektronen am Topkontakt. Weitere detaillierte Untersuchungen an diesen Topkontakten zeigen, dass im Falle von Silber als Metall diese Grenzfläche von Diffusionsprozessen dominiert ist. Im Gegensatz dazu zeigt das unedle Metall Aluminium keine Diffusion und führt zu abrupten Grenzflächen. Im ersten Fall kann zudem eine Monolage vom Molekül auf dem Metallkontakt nachgewiesen werden, die unabhängig von der Metalldicke aufschwimmt. Zuletzt werden Bauelemente oder Teile solcher mit Photoelektronenspektroskopie vermessen. Hierbei werden die Grenzflächendipole, die Ausbildung von Verarmungszonen, die Energieangleichung in Mischschichten und der Einfluss der Eingebauten Spannung untersucht. Es können die Banddiagramme von pn-Übergängen, einfachen pin Homoübergängen, komplexeren pin Heteroübergänge mit Zener-Dioden Verhalten sowie eine gesamte OLED gezeigt werden. Die Ergebnisse erlauben einen tieferen Einblick in die Arbeitsweise solcher Bauelemente.

This thesis is about the development and validation of a numerical model for the simulation of the current-voltage characteristics of organic thin-film devices. The focus is on the analysis of a white organic light-emitting diode (OLED) with fluorescent blue and phosphorescent red and green emitters. The simulation model describes the charge transport as a one-dimensional drift-diffusion current and is developed on the basis of the Scharfetter-Gummel method. It incorporates modern theories for the charge transport in disordered organic materials, which are considered by means of special functions for the diffusion coefficient and the charge-carrier mobility. The algorithm is designed such that it can switch between different models for mobility and calculates both transient and steady-state solutions. In the analysis of the OLED, electron and hole transport are investigated separately in series of single-carrier devices. These test devices incorporate parts of the layers in the OLED between symmetrically arranged injection layers that are electrically doped. Thereby, the OLED layer sequence is reconstructed step by step. The analysis of the test devices allows to obtain the numerous parameters which are required for the simulation of the complete OLED and reveals many interesting features of the OLED. For instance, it is shown how the accumulation of charge carriers in front of an interface barrier increases the mobility and the transfer rate across the interface. Furthermore, it is demonstrated how to identify charge-trapping states. This leads to the detection of deep trap states in the emission zone of the OLED -- an interesting aspect, since these states can function as recombination centers and may cause non-radiative losses. Moreover, various other effects such as interface dipoles and a slight freeze-out of active electric dopants in the injection layers are observed. In the simulations of the numerous test devices, the parameters are consistently applied. Thereby, the agreement between simulation and experiment is excellent, which demonstrates the correctness and applicability of the developed model. Finally, the complete OLED is successfully simulated on the basis of the parameters that have been obtained in the analysis of the single-carrier devices. The simulation of the OLED illustrates the transport levels of electrons and holes, and proofs that the OLED efficiency is low because of non-radiative recombination in the interlayer between the phosphorescent and fluorescent emission zones. In this context, many interesting issues are discussed, e.g. the applicability of the Langevin model in combination with the mobility models for the description of recombination and the relevance of interactions between free charge carriers and excitons.

The scientific research on organic luminescent molecules is a broadly diversified field.In the present work, two topics have received special attention: First, room-tem-perature phosphorescence (RTP) in amorphous organic layers, and second, specialapplications of organic LEDs (OLEDs). Since the phosphorescence as a transition between a triplet and a singlet state is notspin conservative, it is natively very slow and is usually overlaid by non-radiativetransitions. Experiments on triplet states are therefore often performed at low tem-peratures. Escaping this limitation, the topic of RTP arises, wherein biluminescenceis a special case. This means that phosphorescence and fluorescence can be observedsimultaneously and special attention is paid to the interaction of the two processes. After a theoretical and methodological introduction, this work transfers an establishedmethod for the determination of the photoluminescence quantum yield (PLQY) tobiluminescent and RTP systems. Among other things, it was shown that interactionsbetween the states must be taken into account in order to obtain correct results.Different physical competences can and must be combined, for example to detect thesole phosphorescent contribution to the PLQY of a biluminescent system. However,there is no literature on the consideration of statistical measurement uncertaintiesduring the PLQY acquisition itself. This gap could be closed by developing a methodthat cleverly exploits the measurement principle to obtain a broad statistical basis fordata analysis with moderate additional experimental effort. This evaluation methodhas its strength especially in the fact that it is independent of the actually investigatedobject and thus has relevance beyond research on organic emitters. The following chapter deals with more basic properties of RTP, analysing a num-ber of molecules that can be interpreted as fragments of the well-known tetra-N-phenylbenzidine (TPB). Using a combination of optical characterization and quan-tum mechanical simulations, the twisted biphenyl-core of TPB has been identified asthe basic molecular building block for efficient radiative triplet-singlet transitions. The systematics coming with a series of similar molecules, was further used to developa numerical fit routine for biluminescent processes. Different numbers of bromineatoms were synthetically attached to TPB, which creates a heavy-atom effect thatenhances spin flips and thus triplet-singlet transitions. Mathematically, the dynamicsof the transition processes can be described with a system of coupled differentialequations. The core elements therein are the transition rates, which reflect the timeconstants of the corresponding processes. Radiative and non-radiative transitions aswell as intermolecular interactions could be quantified that way. The last part of the thesis deals with the physics of OLEDs and the developmentof particular OLED applications. Especially the concept of AC/DC OLEDs is deep-ened, which allows an operation with alternating current (AC) by a combination ofdirect-current (DC) components. The big advantage of this design is the independentcontrollability of two diodes within one light source. This allows, for example, thecontinuous adjustment of the emission colour over a wide range. Further improve-ments such as transparency and improved colour rendering are the results of thiswork. Finally, the AC/DC strategy was transferred to a completely new application,in which spatially different radiation characteristics are developed and exploited.:Abstract List of Publications List of Abbreviations I Fundamentals 1 Introduction 2 Organic Luminophores 2.1 Physical Basics of Organic Molecules 2.1.1 Molecular Orbitals 2.1.2 Spin States of Molecules 2.2 Transitions 2.2.1 Jablonski Diagrams 2.2.2 Singlet-Triplet Transitions 2.3 Non-Linear Processes 2.3.1 Förster and Dexter Transfer 2.3.2 Bimolecular Annihilation Processes 2.3.3 Other Quenching Mechanisms 2.4 Room-Temperature Phosphorescence and Biluminescence 2.5 Rate Equations for Luminescent Molecules 3 Methods and Techniques 3.1 Materials 3.1.1 Materials for Biluminescence and RTP Experiments 3.1.2 OLED Materials 3.1.3 PLQY Reference Samples 3.2 Sample Preparation 3.2.1 Spin Coating 3.2.2 Thermal Evaporation 3.3 Setups for Photoluminescent characterization 3.3.1 Enterprise 3.3.2 Time-Correlated Single Photon Counting 3.3.3 PLQY Setup 3.3.4 Fluoromax 3.4 Setups for OLED characterization 3.4.1 DC Electroluminescence 3.4.2 AC Electroluminescence 3.4.3 Beam-Shaping Profiles 3.4.4 Transparency 3.5 Line Shape Analysis of Emission Spectra II Biluminescence of Organic Molecules 4 Photoluminescence Quantum Yield (PLQY) Measurements 4.1 Measurement and Evaluation Procedure 4.2 Experimental Influences on the Results 4.2.1 Importance of the B Measurement 4.2.2 Calibration of the Setup 4.2.3 Other Systematic Errors 4.3 Data Evaluation 4.3.1 Subtraction of the Background 4.3.2 Choosing the Wavelengths for Evaluation 4.3.3 Statistical Data Analysis 4.3.4 Reabsorption in the Sample 4.4 Application of PLQY Measurements 4.4.1 PLQY Values of Reference Samples 4.4.2 The PLQY of Biluminescent Samples 4.4.3 Negative PLQY and the Influence of Quenching 5 TPB fragments 5.1 Motivation and Scope of the Experiment 5.2 Spectroscopic Characterization 5.3 Discussion of the Results 6 Brominated TPB as Test Case for Rate Equation Fitting 6.1 Scope and Expectations 6.2 The Heavy-Atom Effect 6.3 Estimation of the ISC Rate 6.4 Rate Equation Fitter 6.4.1 Experimental Input parameters 6.4.2 Determination of𝑘rand𝑘nr 6.4.3 Discussion of the Fit Routine 6.4.4 Data Acquisition and Experimental Influences 6.5 PL Characteristics of the BrxTPB-Series 6.6 Fit Curves and Numerical Values 6.7 Discussion 7 Summary of Part II III Organic Light-Emitting Diodes 8 Introduction and Theoretical Background 8.1 OLEDs in the Framework of This Thesis 8.2 Introduction and Recent Advances 8.3 Organic Semiconductors and Light-Emitting Diodes 8.3.1 Charge Carrier Transport 8.3.2 Organic Diode Structure 8.3.3 Luminescent Measures 8.3.4 The Emission Colour 8.3.5 Efficiency Parameters of OLEDs 9 Advances in AC/DC OLEDs 9.1 Transparent and colour-tunable OLEDs 9.2 Real-Time Beam Shaping OLEDs 9.2.1 The Influence of the Cavity Mode 9.2.2 Angularly Confined Emission 9.2.3 Results and Discussion 10 Angular resolved EQE 11 Summary of Part III Appendix A Low Intensity Noise of the Spectrometer B Calculation of the Density of Triplet States C User Manual for Grape C.1 The Figures C.2 Options C.3 Outputs C.4 Internal Data Processing D TPB-Fragments: Line-Shape Analysis E BrxTPB Fit Curves F Side projects Bibliography Acknowledgements / Die wissenschaftliche Forschung an organischen lumineszenten Molekülen ist ein breitgefächertes Themenfeld. In der hier vorliegenden Arbeit fanden besonders zwei The-men Beachtung: zum einen die Raumtemperaturphosphoreszenz (RTP) in amorphenorganischen Schichten, und zum anderen spezielle Anwendungen organischer LEDs(OLEDs). Da die Phosphoreszenz als Übergang zwischen einem Triplett- und einem Sigulettzu-stand nicht spinerhaltend ist, ist er nativ sehr langsam und wird meist von nicht-strahlenden Übergängen überlagert. Häufig finden Experimente zu Triplettzustän-den daher unter sehr niedrigen Temperaturen statt. Diese Einschränkung entgehend,ergibt sich das Themenfeld der RTP, worin die Bilumineszenz ein Spezialfall ist. Dasbedeutet, dass zeitgleich Phosphoreszenz und Fluoreszenz beobachtbar sind und einbesonderes Augenmerk auf dem Wechselspiel der beiden Prozesse liegt. Nach einer theoretischen und methodischen Einführung, wird in der vorliegenden Ar-beit eine etablierte Methode zur Bestimmung der Photolumineszenzeffizienz (PLQY)auf bilumineszente und RTP-Systeme übertragen. Unter anderem zeigte sich hierin,dass besonders Interaktionen zwischen den Zuständen berücksichtigt werden müssen,um korrekte Ergebnisse zu erhalten. Unterschiedliche physikalische Kompetenzenkönnen und müssen kombiniert werden, um zum Beispiel den alleinigen phospho-reszenten Anteil an der PLQY eines biluminszenten Systems zu detektieren. Aller-dings existiert keine Literatur zur Berücksichtigung statistischer Messunsicherheitenwährend der PLQY Detektion. Diese Lücke konnt durch eine entwickelte Methodegeschlossen werden, die das Messprinzip geschickt ausnutzt, um mit moderatem ex-perimentellem Mehraufwand eine breite statistische Basis zur Datenanalyse zu erhal-ten. Diese Auswertemethode hat ihre Stärke besonders darin, dass sie vom eigentlichuntersuchten Objekt unabhängig ist und damit auch Relevanz jenseits der Forschungan organischen Emittern hat. Im anschließenden Kapitel werden grundlegendere Eigenschaften der RTP behandelt,wobei eine Reihe an Molekülen analysiert wird, die als Fragmente des bekannten tetra-N-phenylbenzidine (TPB) interpretiert werden können. Mit einer Kombination ausoptischer Charakterisierung und quantenmechanischen Simulationen konnte der ver-drillte Biphenylkern von TPB als der grundlegende molekulare Baustein für effizientestrahlende Triplett-Singulett-Übergänge identifiziert werden. Die Systematik, die Serien ähnlicher Moleküle mit sich bringen, wurde weiterhingenutzt, um eine numerische Anpassungsroutine für bilumineszente Prozesse zu ent-wickeln. TPB Moleküle wurden synthetisch mit verschiedener Zahl an Bromatomenversehen, was einen Schweratomeffekt erzeugt, der Spinumkehr und damit auch Trip-lett-Singulett-Übergänge verstärkt. Mathematisch kann die Dynamik der Übergangs-prozesse mit einen System gekoppelter Differentialgleichungen beschrieben werden.Die Kernelemente darin die Übergangsraten, die die Zeitkonstanten der entsprechen-den Prozesse widerspiegeln. In der vorliegendenden Arbeit konnten somit strahlendeund nichtstrahlende Übergänge, sowie intermolekulare Wechselwirkungen quantifi-ziert werden. Der letzte Teil der Arbeit befasst sich mit der Physik und der Anwendung von OLEDs.Besonders das Konzept der AC/DC OLEDs wird dabei vertieft, das durch eine Kom-bination aus Gleichstrombauteilen, einen Betrieb mit Wechselstrom ermöglicht. Dergroße Vorteil dieses Aufbaus ist die unabhängige Ansteuerbarkeit zweier Dioden in-nerhalb einer Lichtquelle. Das erlaubt zum Beispiel die stufenlose Einstellung derEmissionsfarbe über einen weiten Bereich. Weitere Verbesserungen wie Transparenzund eine verbesserte Farbwiedergabe sind Ergebnisse dieser Arbeit. Letztlich wurdedie AC/DC Strategie auf einen völlig neuen Anwendungsfall übertragen, in dem räum-lich verschiedene Abstrahlcharakteristiken entwickelt und ausgenutzt werden.:Abstract List of Publications List of Abbreviations I Fundamentals 1 Introduction 2 Organic Luminophores 2.1 Physical Basics of Organic Molecules 2.1.1 Molecular Orbitals 2.1.2 Spin States of Molecules 2.2 Transitions 2.2.1 Jablonski Diagrams 2.2.2 Singlet-Triplet Transitions 2.3 Non-Linear Processes 2.3.1 Förster and Dexter Transfer 2.3.2 Bimolecular Annihilation Processes 2.3.3 Other Quenching Mechanisms 2.4 Room-Temperature Phosphorescence and Biluminescence 2.5 Rate Equations for Luminescent Molecules 3 Methods and Techniques 3.1 Materials 3.1.1 Materials for Biluminescence and RTP Experiments 3.1.2 OLED Materials 3.1.3 PLQY Reference Samples 3.2 Sample Preparation 3.2.1 Spin Coating 3.2.2 Thermal Evaporation 3.3 Setups for Photoluminescent characterization 3.3.1 Enterprise 3.3.2 Time-Correlated Single Photon Counting 3.3.3 PLQY Setup 3.3.4 Fluoromax 3.4 Setups for OLED characterization 3.4.1 DC Electroluminescence 3.4.2 AC Electroluminescence 3.4.3 Beam-Shaping Profiles 3.4.4 Transparency 3.5 Line Shape Analysis of Emission Spectra II Biluminescence of Organic Molecules 4 Photoluminescence Quantum Yield (PLQY) Measurements 4.1 Measurement and Evaluation Procedure 4.2 Experimental Influences on the Results 4.2.1 Importance of the B Measurement 4.2.2 Calibration of the Setup 4.2.3 Other Systematic Errors 4.3 Data Evaluation 4.3.1 Subtraction of the Background 4.3.2 Choosing the Wavelengths for Evaluation 4.3.3 Statistical Data Analysis 4.3.4 Reabsorption in the Sample 4.4 Application of PLQY Measurements 4.4.1 PLQY Values of Reference Samples 4.4.2 The PLQY of Biluminescent Samples 4.4.3 Negative PLQY and the Influence of Quenching 5 TPB fragments 5.1 Motivation and Scope of the Experiment 5.2 Spectroscopic Characterization 5.3 Discussion of the Results 6 Brominated TPB as Test Case for Rate Equation Fitting 6.1 Scope and Expectations 6.2 The Heavy-Atom Effect 6.3 Estimation of the ISC Rate 6.4 Rate Equation Fitter 6.4.1 Experimental Input parameters 6.4.2 Determination of𝑘rand𝑘nr 6.4.3 Discussion of the Fit Routine 6.4.4 Data Acquisition and Experimental Influences 6.5 PL Characteristics of the BrxTPB-Series 6.6 Fit Curves and Numerical Values 6.7 Discussion 7 Summary of Part II III Organic Light-Emitting Diodes 8 Introduction and Theoretical Background 8.1 OLEDs in the Framework of This Thesis 8.2 Introduction and Recent Advances 8.3 Organic Semiconductors and Light-Emitting Diodes 8.3.1 Charge Carrier Transport 8.3.2 Organic Diode Structure 8.3.3 Luminescent Measures 8.3.4 The Emission Colour 8.3.5 Efficiency Parameters of OLEDs 9 Advances in AC/DC OLEDs 9.1 Transparent and colour-tunable OLEDs 9.2 Real-Time Beam Shaping OLEDs 9.2.1 The Influence of the Cavity Mode 9.2.2 Angularly Confined Emission 9.2.3 Results and Discussion 10 Angular resolved EQE 11 Summary of Part III Appendix A Low Intensity Noise of the Spectrometer B Calculation of the Density of Triplet States C User Manual for Grape C.1 The Figures C.2 Options C.3 Outputs C.4 Internal Data Processing D TPB-Fragments: Line-Shape Analysis E BrxTPB Fit Curves F Side projects Bibliography Acknowledgements

Das Hauptziel dieser Arbeit war ursprünglich die Umsetzung des Konzeptes des Bipolartransistors mit organischen Halbleitern. Obwohl dieses elektronische Bauteil eine Grundfeste klassischer Elektronik darstellt, war es bislang nicht möglich Stromverstärkung mit organischen Halbleitern nachzuweisen. Das Prinzip des Bipolartransistors ist eng verknüpft mit der Diffusionslänge der Minoritätsladungsträger. Aufgrund der amorphen Struktur typischer organischer Materialien, sind Diffusionsprozesse in der Regel stark unterdrückt. Eine mögliche Lösung sind organische Halbleiterkristalle, welche aufgrund ihrer Ordnung signifikant längere Diffusionslängen gewährleisten sollten. Der erste Teil dieser Arbeit untersucht Wachstumsmethoden unterschiedlicher Kristallkonfiguration des Halbleiters Rubrene in Dünnschichtform. Ein besonderer Fokus liegt hierbei auf dem Einfluss von Dotierung auf den Kristallisationsprozess. Drei der Kristallphasen werden auf optimale Reproduzierbarkeit optimiert und umfangreich mit strukturellen Methoden untersucht. Die Strukturanalyse wird erweitert durch Untersuchungen des vertikalen Leitungsverhaltens der unterschiedlichen Kristallphasen in reiner, lochdotierter und elektronendotierter Form. Dünne Schichten aus Rubrene in der triklinen Kristallform zeigen hierbei Rekordwerte für die vertikale Beweglichkeit. Der zweite Teil dieser Arbeit untersucht elektronische Bauelemente basierend auf diesen Kristallen. Zunächst werden organische Schottky, pn und pin Dioden analysiert sowie der Einfluss der einzelnen Schichten auf die elektrischen Eigenschaften der Bauelemente. Als eine mögliche Anwendung dieser Dioden werden Halbwellengleichrichter untersucht, welche im Bereich über 1 GHz operieren können. Diese stellen somit die zur Zeit schnellsten organischen Halbleiterbauelemente dar. Des Weiteren werden organische Feldeffekttransistoren in lateraler und vertikaler Ausführung untersucht, um den Nutzen dieser Kristallschichten für moderne Transistorkonzepte zu verdeutlichen. Schlussendlich werden Konzepte zur Realisierung eines organischen Bipolartransistors untersucht. Darauf basierend wird das erste Bauelement dieser Art vorgestellt, welche funktionierende Stromverstärkung zeigt. Dies stellt den ersten Schritt in der Untersuchung einer neuen Klasse an organischen Bauelementen dar. Des Weiteren bietet es neue Möglichkeiten der Untersuchung fundamentaler Eigenschaften, im Speziellen im Bezug auf Minoritätsladungsträgerdiffusion. / The main motivation of this thesis was originally the realization of the Organic Bipolar Junction Transistor (OBJT), an electronic device that has not been shown in literature yet. Its functionality is intimately tied to minority charge carrier diffusion. However, diffusion lengths are usually low in amorphous organic semiconductors. Thus, methods regarding the growth and doping of thin-flms of crystalline rubrene crystals are investigated. The higher degree of order provided by crystals makes longer diffusion lengths possible. The first part of this thesis studies the growth of different crystal polymorphs of rubrene on various substrates and changing conditions, including the infuence of doping on the growth process. Three crystal phases are optimized for reproducible processing and investigated via structural measurements. The analysis of the crystal properties is followed up by a study of vertical conduction properties of pristine, p-doped, and n-doped crystals. All three types of crystals are successfully doped. The analysis reveals record-high vertical charge carrier mobilities for the triclinic polymorph of the thin-film form of rubrene. The second part of this thesis presents electronic devices based on these layers. At first, organic Schottky, pn, and pin diodes are discussed, including the influence of the individual layers on the electric properties. As an exemplary application, half-wave rectifier operating in the GHz-regime are studied, representing the fastest organic electronic device to date. Furthermore, Organic Field-Effect Transistors (OFETs) and Vertical Organic Field-Effect Transistors (VOFETs) based on these crystalline thin-őlms are made, showing promising properties in the field of vertical transistor designs. The last chapter presents investigations of several designs, stacks, and geometries regarding OBJTs. The worlds first functioning OBJT is developed, showing ampliőcation of the input-current. It is the őrst step towards an entirely new class of organic devices, offering not only new technological opportunities but new aspects of physics in regard to minority carrier diffusion as well. / Hłowny zaměr tutoho doktorskeho dzěła je realizacija prěnjeho bipolarneho transistora na zakładźe organiskich połwodźakow. Byrnjež je tuta komponenta jedna z najwažnišich a najstaršich w polu klasiskeje elektroniki, njeběše hač dotal móžno priběranje sylnosće na zakładźe milinoweho pruda pokazać. Princip bipolarneho transistora je wusko zwjazany z konceptom diffuzije minoritnych nabitkow. Organiske materialije su zwjetša amorfne, štož na difuziju bazowace procesy potłóči. Problem hodźi so rozrisać hdyž so wužija organiske połwodźace kristale kotřiž jich wjetšeho porjada dla, dlěšu difuziju zmóžnja. Prěni dźěl dźěła wopisa wšelakore konőguracije kristalow organiskeho połwodźa-ka rubren w formje ćenkich worštow. Wosebity fokus leži při tym na dotěrowanju kristalow a wliw dotanta na kristalizaciju. Tři wuzwolene polymorfy so op-timěruja a wobšěrnje strukturelnje přepytuja. Dale so elektriske kajkosće wšěch třoch kristalnych fazow přepytuja na zakładźe intrinsiskich, p-dotěrowanych a n-dotěrowanych kristalow. Trikliniske kristale pokazuja rekordne hódnoty za wertikalnu pohibliwosć. Druhi dźěl wobjednawa elektroniske komponenty na bazy tutych kristalow.Schottky, pn a pin diody na zakładźe rubrena so prezentuja, kaž tež wliw jed-notliwych worštow na elektriske kajkosče. Jako prikład so jednore wusměrjaki pokazaja, kotřriž hodźa we wobłuku ultra-wysokich frekwencow nałožować. Potajkim jedna so wo najspěšniše organiske komponenty po nětcišim stawje wedomosće. Dale so organiske transistory na bazy pólneho efekta přepytuja, kotřiž pokazaja hódnosć tutych worštow za elektroniske komponenty kotřiž wužija lateralny a wertikalny transport zromadnje. Posledni dźěl wobjednawa eksperimenty na polu organiskich bipolarnych transistorow. Wopisa so prěni organiski elektroniski element, kiž pokaza posylnjenje signala na zakładźe miliny. Je to prěni krok přepytowanja noweje klasy organiskeje elektroniki, kiž skiči nowe metody přepytowanja fundamentalnych procesow w tutych materialijach.